As writers, we often find it uncomfortable to write with an identifiable voice. I know that I find it easier to write correctly than to get a little sassy or humorous or silly or staid. Even though the voice for a particular piece may call for you to try out a new version of your voice, you may feel weird doing it.
You should always shoot for the voice that will work best for the topic, while maintaining your true voice. Here are some ways to approach it.
1. Practice. It’s important to write through the discomfort. There isn’t any reason you have to sit down and pound out a final version right this minute. Take some time to quiet the discomfort you feel at approaching a topic or a style that’s new to you.
2. Practice writing in extremes. Write a piece as outrageously or as straight as possible. If you practice with the extremes, you’ll desensitize yourself to the discomfort. Next time, there will be less fear.
3. Take that outrageous version of your piece and tweak the tone of it a little at a time until you find the voice that is just right for the piece and the audience.
4. The voice you use in your writing will always be your own, but it will vary for each piece. It’s like the difference in a piano player’s approach to a classical piece versus a jazz piece.
When I’m working with voice in a piece of writing, it helps me to think in terms of not transforming my voice completely, but in terms of bending the edges of my writing to achieve the subtle difference needed.
Before You Write - Lou Belcher 
I find talking aloud helps, as if I’m giving a speech. Often I can hear where the voice falters, or where it’s less than interesting. I read my whole novel aloud at least once, so that I can hear both the characters and the narrator speaking.
Great technique….
Lou